The genus Hypanus formerly was a junior synonym of Dasyatis (Kottelat, 2013); it was resurrected by Last et al. (2016) in their revision of the family Dasyatidae.

The nomenclature of this species is often confused, occasionally resulting in the listing of brevis and dipterurus as separate species. Both Jordan and Gilbert and Garman published descriptions of this species in the same year, 1880. However, Jordan and Gilbert published their account of specimens from San Diego in May of 1880, while Garman published his description in October of that year. Garman (1913) subsequently overlooked these facts and inappropriately synonymized dipterurus with brevis. However, Jordan and Gilbert's description has precedence and is recognized as the original by the American Fisheries Society and Eschmeyer's Catalog of Fishes. The species originally described as Dasyatis hawaiiensis Jenkins, 1903 from Hawaii was later synonymized as Dasyatis (=Hypanus) dipterurus (Nishida and Nakaya 1990). Additional taxonomic work on the Hawaiian dasyatids is necessary to further clarify the relationships of these stingrays to the eastern Pacific fauna.

Justification:
This is an amended version of the 2006 assessment to accommodate the recent change in genus name from Dasyatis to Hypanus.

Hypanus dipterurus is a broadly distributed but poorly known stingray from the eastern Pacific. Biological and fishery information is primarily available from México where H. dipterurus is commonly landed among artisanal elasmobranch fisheries and frequently taken as bycatch in trawl fisheries (especially by shrimp trawlers). Populations from the Mexican Pacific display seasonal movement patterns related to reproductive events, but no information is available on trends in abundance. Recent studies indicate that this stingray is relatively long lived (to at least 28 years), has a low fecundity (1 to 4), and a low intrinsic rate of increase. Female growth rates are estimated to be among the lowest reported for any batoid. These combined factors indicate that H. dipterurus populations are of low productivity and demonstrate limited resilience to fishing pressure. Due to its vulnerability and importance within the unregulated artisanal elasmobranch fishery, this stingray is considered Near Threatened in México. Based on the lack of information pertaining to the biology, distribution, and fisheries for this species throughout the majority of its range, H. dipterurus is classified as Data Deficient in the USA as well as Central and South America. Where is it taken in fisheries in those regions it may prove to be at risk when more information is available.

Reports of this stingray from British Columbia, Canada (Hart 1973) are questionable and have not been verified. If accurate, they represent anomalies, as H. dipterurus is typically a subtropical to tropical species. The confirmed range is from southern California, USA to Chile (where it is occasional only); including the Galápagos and Hawaiian Islands (Eschmeyer et al. 1983, Nishida and Nakaya 1990, Lamilla et al. 1995).

Rough estimates of H. dipterurus abundance were calculated by Mathews and Druck-Gonzalez (1975) from the Bahía Magdalena lagoon complex, Baja California Sur, México based on trawl surveys. These authors noted a distinct seasonal trend in abundance within the lagoon complex and estimated 112,000 individuals present in February, increasing to 378,000 in August. Species identifications were problematic and these estimates may include H. longus or urotrygonid rays. In the Gulf of California, exploratory trawl surveys indicated that H. dipterurus comprised 26% of the total demersal catch weight (Flores et al. 1995). No details on the abundance of this species outside of México are available.

In Chile, the southern extent of the species' distribution, and southern California, the northern extent of its distribution, this species is rare. In Chile, it is known only from three specimens taken in the north (Antofagasta). Its occurrence in these extremities of its range appears to be linked to suitable climatic conditions due to El Niño (Lamilla, et al. 1995, Ebert, 2003).

Hypanus dipterurus is a demersal stingray known primarily from relatively shallow, inshore waters over sand and mud bottoms or near rocky outcrops and kelp beds (Feder et al. 1974, Eschmeyer et al. 1983). Off southern California, the species has been reported to occupy shallow waters (intertidal to 7 m) in the summer and moves to depths of 13 to 17.7 m during the late fall and winter months (Feder et al. 1974). In Chile the species has been reported at depths of 3 to 30 m. However, Chave and Mundy (1994) reported H. dipterurus from depths of 52 to 150 m over sand bottoms in the Hawaiian archipelago. The Hawaiian records may represent a misidentification or indicate that a much broader depth range may be potentially utilized by this species.

The limited biological information available for H. dipterurus is derived primarily from the Bahía Magdalena lagoon complex, Baja California Sur, México. These parameters may differ markedly throughout the species' range. In the Bahía Magdalena lagoon complex, courtship and insemination is thought to occur in the late summer during July and August (Mariano-Melendez 1997). Sperm storage or diapause may contribute to delayed development of embryos and gestation is suggested to occur over 2 to 2.5 months with pupping taking place the following summer (July-September) in shallow estuaries (Mariano-Melendez 1997). Reproduction appears to be annual and litter sizes range from one to four pups (Mariano-Melendez 1997, Smith 2004). Reproductive mode is aplacental viviparity in which embryos are nourished by a combination of a small yolk-sac and histotrophe secreted from the uterus (as with all myliobatoid rays). Only a single ovary is functional. Maximum size is ~100 cm disc width (DW) (McEachran and Notarbartolo-di-Sciara 1995) and size at birth ranges 18 to 23 cm DW (Mariano-Melendez 1997, Smith 2004). The median size at maturity is estimated to be 58.5 cm DW (males) and 43.4 cm DW (females). Growth estimates based on vertebral ageing indicate that these sizes correspond to ages of 10 years in females and seven years in males (see life history parameters below for other maturity estimates). Age analysis indicates slow growth rates and maximum observed ages up to 28 years. Von Bertalanffy models estimate growth coefficients of 0.55 y-1 for females and 0.10 y-1 for males (Smith 2004). Females attain greater sizes and ages than males. Catch records suggest that the species may segregate by size and sex (Mathews and Druck-Gonzalez 1975, Smith 2004).

Diet is comprised primarily of infaunal organisms and large feeding pits are excavated by jetting water and through movements of the pectoral fins. Some epibenthic species are also taken. In the Bahía Magdalena lagoon complex, pea crabs (Pinnotheridae), razor clams (Solyema valvulus) and polychaetes are the primary prey items, in order of decreasing importance (Bizzarro 2005).

Directed artisanal fisheries and incidental catch among trawl fisheries and other artisanal fisheries using gillnets, longlines, or traps.

Hypanus dipterurus represents a primary component of artisanal elasmobranch fishery catches of the Pacific coast of México and the Gulf of California (Bizzarro et al. 2000, R. Hueter et al. unpublished data, Smith 2004, Bizzarro 2005). Its contribution to the fishery is likely underestimated due to the lack of species-specific landing information and potential misidentification. Although present in artisanal landings throughout the year, catches of this stingray are highest during the summer and fall (Notarbartolo di Sciara 1987; Bizzarro et al. 2000). Hypanus dipterurus is the second most abundant batoid landed in coastal waters of Sonora, México, comprising ~19% of all batoid landings in seasonal surveys conducted in 1998 and 1999 (R. Hueter et al., unpublished data, Márquez-Farías 2002). This species is targeted during primarily summer months in Bahía Almejas, located in the southern portion of the Bahía Magdalena lagoon complex, Baja California Sur, México. In this embayment, it is most abundant batoid species landed in August (~43%) and the fourth most abundant batoid in June landings (~8%) (Bizzarro 2005). Individuals are primarily captured in demersal gillnets in which their tail spines are entangled. This method of entanglement allows a wide range of mesh sizes to be effective for capturing juveniles as well as adults. Juveniles comprised the majority of individuals landed in the Bahía Magdalena lagoon complex artisanal elasmobranch fishery during 1998-2000 (Smith 2004, Bizzarro 2005, Bizzarro and Smith in preparation).

Based on records from exploratory fishing surveys, it is likely that this species represents a significant component of trawl bycatch fisheries (especially shrimp trawl bycatch) in the Mexican Pacific (Mathews and Druck-Gonzalez 1975, Flores et al. 1995). No information is available on the species' actual contribution to bycatch in other artisanal or trawl fisheries in México, or through its Central and South American range.

Many coastal embayments and mangrove lagoons in north Pacific México, which serve as habitat for D. dipterura, are being altered for the purpose of shrimp farming. Although these activities are presently limited, their expected increase could detrimentally alter suitable habitat for this species (Bizzarro pers. obs).

Hypanus dipterurus fisheries and bycatch are unmanaged throughout the species range. In México, a moratorium on the issue of elasmobranch fishing permits was enacted in 1993, but no formal management plan has been implemented. However, legislation is currently being developed in México to establish national elasmobranch fishery management. Elasmobranch fisheries are unmanaged throughout Central and South America. Attempts to monitor and regulate fisheries in the eastern tropical Pacific would greatly improve conservation of H. dipterurus and other chondrichthyans.

Elasmobranch landings reported from México and Central America typically lack species-specific details. Large sharks are generally grouped as "tiburónes" and small sharks as "cazonés" while batoids are often simply termed "manta raya" collectively. Mexican federal fisheries agencies recently began providing slightly more taxonomic resolution of ray landings by listing several new categories. Landings of H. dipterurus, however, may still be unknown as they are grouped in the modified category of "manta raya" that may include dasyatid as well as urotrygonid and mobulid species. Additional monitoring of artisanal elasmobranch fisheries and commercial trawl bycatch on a species-specific basis is critical for detecting trends in effort, abundance, and catch of elasmobranchs. Concise guides to species identification for both fishermen and fisheries biologists would be a valuable aid for improving the monitoring of these landings. Fishery-independent surveys of this and other demersal elasmobranchs are necessary to provide estimates of abundance and biomass.

In addition to species-specific catch details, life history information including age, growth, longevity, movement patterns, habitat use, diet, and further reproductive studies from other portions of the species range are necessary to develop effective conservation actions for H. dipterurus. Direct estimates of fishing and natural mortality are critical for assessing the impact of fisheries on a species and would greatly improve population models of this vulnerable species.

The development and implementation of management plans (national and/or regional e.g., under the FAO International Plan of Action for the Conservation and Management of Sharks: IPOA-Sharks) are required to facilitate the conservation and sustainable management of all chondrichthyan species in the region. See Anon. (2004) for an update of progress made by nations in the range of H. dipterurus.